The invention relates to a duct system, especially for use as an intake manifold for an internal combustion engine, which has flap valves in the individual intake passages leading to the cylinders. Moreover, the invention relates to a method for the manufacture of the above-mentioned intake manifold.
An arrangement of flap valves in the individual intake passages of an intake manifold is disclosed for example in DE 38 43 509. Each of the cylinders has two separate intake passages for the combustion air. With the flap valves it is possible to close one of the intake passages to the cylinders, so that when the motor is in the partial-load range, the effective air intake cross section for the cylinders can be reduced. The actuation of the flap valves can be performed through a push rod which is operated by a flap valve drive means. The flap valves move against a mechanical stop. Thus the flap valve can only be in the open or closed position. The elasticity of the push rod is deliberately utilized to compensate for production tolerances by deforming when the flap valves are in the abutted position.
It is a disadvantage of the known system that the flap valves can assume only two working positions. However, continuous adjustability of the flap valves with defined flap valve positions would be desirable. For a continuous variation of the flap valves, the equalization of tolerances by the resilient push rod must be omitted. This would be possible only if the intake manifold were manufactured with very small tolerances.
This is not possible, however, due to economic considerations.
The object of the invention is to provide an intake tube with a continuously variable flap valve which can compete in economics of production with the known flap valve manufacturing methods. This object is achieved by the features of the invention as described and claimed hereinafter.
The intake manifold according to the invention has flap valves which are disposed in the intake passages of the intake manifold between the intake plenum and the outlet on the cylinder side. The flap valves are operated by gears or toothed sectors. A drive means applies the operating force, for example via a rack, through the control to the flap valves. The drive means must assure the possibility of a continuous operation of the flap valves. The mechanical couplings between the operating rods, the flap valves and the drive means must be constructed without free play. Only in this way can a precisely defined flap valve position be achieved. In order for all of the flap valves to always have the same position relative to each other, any manufacturing tolerances in the intake manifold and in the flap valve system must be compensated. For this purpose an adjustment is provided which can be integrated into the teeth between the rack and the gear wheel or into the flap valve shaft. The adjustment must be designed so that the position of each individual flap valve can be adjusted and then fixed.
If the flap valves are disposed in the vicinity of the cylinder inlets, the precisely defined flap valve position can be utilized to generate a swirling flow in the combustion chamber of the cylinders. This has the advantage of better mixing in the partial-load range of the motor, so that fuel consumption and pollutant emission can be reduced. The continuous adjustability furthermore makes it possible to provide flap valves in all of the intake passages leading to the cylinders. In that case, of course, not all of the flap valves can be closed, since in this case the air supply would be completely cut off.
A practical embodiment of the invention provides the tolerance compensating device on the rack or worm. It then is comprised of a drive rod which is connected to the drive means and is provided with teeth or a sleeve bearing a worm for each flap valve, it being possible for the sleeves to shift freely and to be locked in place on the drive rod. The adjustment can be performed on the gears and toothed sectors precisely in this manner if they are manufactured as base bodies with attached teeth. The integration of the adjustments on these components has the advantage that the connections are easily accessible during assembly. Also, readjustments can easily be carried out in this manner during maintenance operations by releasing the connections on the adjusters.
However, advantages are also to be found if the adjusters are permanently fixed adhesive connections. The adhesive can then be applied during the assembly process and thereafter the entire flap valve control unit assembled. Manufacturing tolerances are thus automatically compensated since the adhesive is not yet cured. After the adhesive connection has cured, the flap valves have become fixed in their defined relation to one another.
In another variant of the invention the adjustment is provided in the mechanical coupling between the flap valve axle and the gear wheels acting as drive means. The flap valve crank can be inserted into a bore in the axis of the flap valve, for example. The bonding of the two components to one another can be accomplished by adhesive bonding. The joint can be made advantageously elastic. Since when the flap valves are in positions between the abutments only low forces act between the flap valves, a definite position within the adjustment range of the flap valves is assured despite the elasticity of the adhesive joint. However, when the flap valves are positioned against the stops, the elasticity of the adhesive joint permits an additional compensation of tolerances. This method thus combines the advantageous principles of the operation of known systems with those of the invention.
In one particular embodiment, the flap valves that are used are assembly-injection molded flap valve modules which can be attached to the intake pipe. This measure increases the economy of the invention.
In order to manufacture the intake manifold of the invention, a method is proposed which permits an efficient adjustment of the flap valves during assembly. This is achieved by the use of a jig which brings the flap valves into the desired position relative to one another and relative to the drive means. After the pre-assembly of the operating linkage and drive means the adjustments can be locked up. Thus the flap valves become invariable in their position with respect to one another. Any manufacturing tolerances are automatically compensated. At the end of the assembly operation the jig is removed again.
These and additional features of preferred embodiments of the invention will be found not only in the claims but also in the description and the drawings, the individual features being applicable individually or jointly in the form of subcombinations in the embodiment of the invention and in other fields and may represent advantageous as well as independently patentable embodiments, for which protection is hereby claimed.